Generally, in large commercial vehicles such as trucks and buses having great weight, an air brake system having excellent braking force, less failure, and easy handling has been used.
An air brake system utilizes air pressure of the compressed air so as to obtain a large braking force by small pedal stepping force. In such a brake system, air compressed by an air compressor is stored in an air tank, two inlets of a dual brake valve are connected to the air tank, two outlets of the dual brake valve are connected to the brake chambers of the front and rear wheels, and a front wheel brake unit and a rear wheel brake unit are connected to the output shafts of each brake chamber.
The dual brake valve is a valve which supplies the compressed air from the air tank to the brake chambers of the front and rear wheels when a driver steps on the brake pedal, and has a double structure which simultaneously connects the flow of air to the front and rear wheels or blocks the flow or air.
In the case of an air brake system of a large commercial vehicle, two independent pressure supply circuits are provided for rules of safety regulations to independently transfer the air pressure to the front and rear wheels through a dual brake valve when braking the vehicle.
Therefore, the air pressure is independently transmitted to the circuit of the front wheel brake unit and the circuit of the rear wheel brake unit via the dual brake valve or blocked at the same time, and even if an error occurs in any one circuit of them, the other circuit is still maintained to ensure the braking safety.
On the other hand, when the driver steps on the brake pedal to perform a braking input, the feeling received via the brake pedal is referred to as a braking feeling, and it is possible to feel the braking feeling such as hard, fully-sinking, pushing, and sticking via the brake pedal.
Such braking feeling is determined by a relation, such as a control feeling (pedal stroke and vehicle deceleration) felt by the pedal stroke to the vehicle deceleration and an effective feeling (pedal effort and vehicle deceleration) felt by a pedal effort to the vehicle deceleration.
Braking of the large commercial vehicle to which the air brake system is applied as described above uses the air pressure as a boost mediator, and a specific pedal ratio is determined in consideration of the characteristics (pedal stroke & effort & pressure) of the dual brake valve and the preferred braking feeling of the driver at the time of design of the vehicle.
FIG. 1 is a perspective view of a brake pedal module, which illustrates a brake pedal 1 operated by a driver for braking input, a dual brake valve 2 which controls the air supply/block to the front wheel and rear wheel brake chambers from the air tank in conjunction with the operation of the brake pedal 1, a pedal plate 3 to which the brake pedal 1 and the dual brake valve 2 are mounted, and a pedal shaft 4 which is rotatably mounted to the pedal plate 3 and is coupled so as to support the brake pedal 1.
When a driver operates the brake pedal 1, a pedal operation force is transmitted to the dual brake valve 2 through a transmission shaft 5, and thus, the actuation of the dual brake valve 2 is performed to transmit the compressed air from the air tank to the brake chambers of the front and rear wheels by the movement of the inner piston.
FIG. 2 is a diagram illustrating a pedal ratio of the brake pedal, in which, a value of A/B is a pedal ratio, and the pedal ratio is fixed to a specific value depending on the vehicle model.
The braking feeling differs depending on the pedal ratio, and FIGS. 3A-3B illustrate that the braking control feeling felt according to a relationship between the pedal stroke and the vehicle deceleration of the braking feeling, and the braking effective feeling felt according to a relationship between the pedal effort and the vehicle deceleration are different depending on the vehicle model due to the fixed pedal ratio.
However, since the pedal ratio is fixed to a specific value depending on the vehicle model, there may be dissatisfaction in the braking feeling depending on the user, and in particular, a large number dissatisfactions of the control feeling (pedal stroke and vehicle deceleration) in the braking feeling have been raised.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.